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The findings, which appear in the scientific journal "Blood," detail how certain proteins in the body direct the creation of new white blood cells.

"All of our blood comes from stem cells in the bone marrow," said Xiao-Hong Sun, Ph.D., the paper's senior author. "And as those cells develop, they branch out into different, more specific types of blood cells."

Sun's lab found there's a point in the creation of new white blood cells where they can become either infection-fighting B or T cells in the immune system or bacteria-eating cells called microphages.

"Now we know at what stage we can switch the development path of the cells," Dr. Sun said. "This is significant because we can use the information to help maintain the balance needed for a healthy immune system."

Sun said that it could be particularly useful in treating elderly patients, who have an increased susceptibility to infections.

The research was funded by a grant from the National Institute of Allergy and Infectious Disease.